Chimpanzee taxonomy remains an active area of research. Four subspecies are commonly recognized: the West African Chimpanzee Pan troglodytes verus; the Nigeria-Cameroon Chimpanzee P. t. ellioti; the Central Chimpanzee P. t. troglodytes; and the Eastern Chimpanzee P. t. schweinfurthii. Recent mitochondrial DNA work (Gonder et al. 2006) shows that schweinfurthii is embedded in troglodytes, and suggests that there are only two major clades of chimpanzees: Pan troglodytes ellioti in West Africa and P. t. troglodytes in Central and East Africa. Based on recent nuclear DNA work, as well as considerations of the overall similarity in behaviour and morphology of the proposed subspecies, Fischer et al. (2006) argue that differences between chimpanzee populations are too small to warrant subspecific designations. While the appropriate taxonomic labelling for different chimpanzee populations remains unresolved, the relative importance of different threats faced by chimpanzees varies across Africa, making a regional approach valuable for conservation purposes. We, therefore, use a four-subspecies classification system here, recognizing that future work may lead to a consensus recognizing more or fewer subspecies.

Justification:
Due to high levels of exploitation, loss of habitat and habitat quality as a result of expanding human activities, and disease (Ebola), this subspecies is estimated to have experienced a significant population reduction in the past 20 to 30 years (one generation is estimated to be 20 years: Boesch and Boesch-Achermann 2000, Emery Thompson et al. in prep., Gombe long-term records, unpubl.) and it is suspected that this reduction will continue for the next 30 to 40 years. The maximum population reduction over a three-generation (i.e., 60 year) period from the 1970s to 2030 is suspected to exceed 50%, hence qualifying this taxon for Endangered under criterion A4. The causes of the reduction, although largely understood, have certainly not ceased and are not easily reversible. The suspected future continuation of the population reduction is a precautionary approach based on the rapidly increasing human population density in the region and the high degree of political instability in the range states. There is evidence that Ebola will continue to spread (Walsh et al. 2005, Lahm et al. 2006) and it is too early to judge whether or not chimpanzee populations will recover from the extremely high levels of Ebola-induced mortality. Recovery will take a very long time even in ideal conditions of complete protection from hunting.

Chimpanzees are found predominantly in moist and dry forests, and forest galleries extending into savanna woodlands. They are omnivorous, and their diet is highly variable according to individual populations and seasons. Fruit comprises about half the diet, but leaves, bark, and stems are also important. Mammals comprise a small but significant component of the diet of many populations. Chimpanzees form social communities of 5 to 150 animals. Home ranges are larger in woodland forest mosaics than in mixed forest, and average 12.5 km² (range 5 to 400 km²).